The present invention relates to a magnetic storage cell and a magnetic memory device using the same.
Conventionally, in magnetic memory devices such as MRAM (Magnetic Random Access Memory) and the like, magneto-resistive elements such as a TMR element (tunnel magneto-resistive element) and the like are used as magnetic storage cells (see JP-A-2001-236781 and JP-A-2001-266567 (these correspond to U.S. patent application Publication No. 2002/0006058.) and the like).
Such magnetic memory devices are exemplified by JP-A-2001-236781 and JP-A-2001-266567 which disclose a plurality types of magnetic memory devices which have magnetic storage cells, each of which is comprised of a pair of TMR elements, and differentially amplify outputs from two TMR elements in pair to generate a read output. In these magnetic memory devices, a write is always performed in a complementary manner such that one of the TMR elements has a free layer (a magnetic layer, the magnetization direction of which changes depending on an external magnetic field) and a pinned layer (a magnetic layer, the magnetization direction of which is fixed), that have the magnetization directions in parallel with each other (i.e., the TMR element has a low electric resistance), while the other TMR element has a free layer and pinned layer that have the magnetization directions in antiparallel with each other (i.e., the TMR element has a high electric resistance). Then, the outputs of the two TMR elements are differentially amplified and read, thereby removing in-phase noise in the read output and therefore improve the S/N ratio.
In a magnetic memory device disclosed in FIG. 6 of JP-A-2001-236781 (hereinafter called the “first prior art example”), a pair of TMR elements which make up a magnetic storage cell are disposed in a direction along a laminating surface with respect to each other. In the first prior art example, the pair of TMR elements have their pinned layers, the magnetization direction of which are set to be in parallel with each other (in the same orientation). Also, in the first prior art example, the pair of TMR elements have their free layers and pinned layers laminated in the same order as each other. Further, one of the TMR elements in pair is provided with two write lines which generate a current magnetic field (a magnetic field induced by applying a current) that causes a change in the magnetization direction of the free layer in the one TMR element. The two write lines are disposed on both sides thereof in the laminating direction with respect to the one TMR element, and sandwiches the one TMR element. Also, the other one of the pair of TMR elements is provided with two write lines, different from the aforementioned write lines, which generate a current magnetic field that causes a change in the magnetization direction of the free layer in the other TMR element. These two write lines are disposed on both sides thereof in the laminating direction with respect to the other TMR element, and sandwiches the other TMR element. Then, in the first prior art example, the respective directions of currents applied to a total of four write lines, which comprise the two write lines provided for the one TMR element and the two write lines provided for the other TMR element, are set to independently control the magnetization directions of the free layers in the pair of TMR elements, thereby implementing the aforementioned complementary write for a single magnetic storage cell.
In a magnetic memory device disclosed in FIG. 10 of JP-A-2001-236781 (hereinafter called the “second prior art example”), a pair of TMR elements which make up a magnetic storage cell are disposed in a laminating direction to each other. Like the first prior art example, in the second prior art example, the pair of TMR elements also have their pinned layers which are set to have the magnetization directions parallel with each other (in the same orientation). Also, in the second prior art example, the pair of TMR elements also have their free layers and pinned layers laminated in the same order as each other, like the first prior art example. Further, in the second prior art example, a single write line is provided commonly for both the TMR elements in the pair, another write line is provided for one of the pair of TMR elements, and a further write line is provided for the other of the pair of TMR elements. Then, the magnetization direction of the free layer in the one TMR element is changed by a current magnetic field generated by the one write line provided commonly for both the TMR elements in the pair and the one write line provided for the one TMR element. The magnetization direction of the free layer in the other TMR element is changed by a current magnetic field generated by the one write line provided commonly for both the TMR elements in the pair and the one write line provided for the other TMR element. The one write line provided commonly for both the TMR elements in the pair is disposed between the pair of TMR elements, the one write line provided for the one TMR element is disposed on one side of the one TMR element opposite to the other TMR element, and the one write line provided for the other TMR element is disposed on one side of the other TMR element opposite to the one TMR element. Then, in the second prior art example, the respective directions of currents applied to the total of three write lines are set to independently control the magnetization directions of the free layers in the pair of TMR elements, thereby implementing the aforementioned complementary write to a single magnetic storage cell.
In a magnetic memory device disclosed in FIG. 2 of JP-A-2001-266567 (hereinafter called the “third prior art example”), a pair of TMR elements which make up a magnetic storage cell are disposed in a laminating direction to each other in a manner similar to the first prior art example. The third prior art example is also similar to the first prior art example in that the pair of TMR elements have their pinned layers which are set to have the magnetization directions parallel with each other (in the same orientation). Also, in the third prior art example, the free layers and pinned layers in the pair of TMR elements are laminated in reverse orders to each other, so that the free layers in the pair of TMR elements are laminated to be in close proximity to each other. These free layers are antiferromagnetically coupled to each other by a non-magnetic conductive layer laminated therebetween. Further, in the third prior art example, two write lines are provided commonly for both of the TMR elements in the pair, such that the pair of TMR elements are entirely sandwiched by the two write lines on both sides thereof in the laminating direction. The magnetization directions of the free layers in the pair of TMR elements are changed by a current magnetic field generated by the two write lines. Then, in the third prior art example, the directions of currents applied to a total of two write lines are set to collectively control the magnetization directions of the free layers in the pair of TMR elements, thereby implementing the aforementioned complementary write for a single magnetic storage cell.
However, in the first to third prior art examples, the magnetization directions of the free layers in a pair of TMR elements, which make up a single magnetic storage cell, are changed by a current magnetic field generated by a plurality of write lines to store information in the magnetic storage cell, but these prior art examples fail to form a magnetic path which efficiently guides the current magnetic field. Therefore, the conventional magnetic memory devices which have magnetic storage cells, each of which is made up of a pair of TMR cells as in the first to third prior art examples, suffer from a large loss of current magnetic field, and therefore fail to efficiently carry out the magnetization reversal of each free layer.
Generally, magnetic memory devices are basically required to reduce the area occupied by magnetic storage cells to increase the storage capacity, to be simple in structure, and to be easy to manufacture.